In season 9, the show is transitioning from the original premise (Charlie, Alan, and Jake) to the later premise where the show continues with Charlie and Jake. This transition might involve some character development for Charlie and Jake. For example, Charlie could be trying to mature, and Jake is becoming more responsible. However, without Alan, the dynamic changes. The writers had to create new storylines, perhaps focusing on the brothers dealing with everyday life, their jobs, relationships, and other supporting characters like the neighbor across the hall, Lyndsey.